Spark plug insulators containing zno



Aug. 2 7, 1957 H. e. SCHURECHT 2,804,392

SPARK PLUG INSULATORS CONTAINING ZnO Filed April 25, 1952 4 Shets-Sheet 1 INVENTOR Ha'rrg G Jchurecbf ATTO RNEY- Aug. 27, 1957 H. G. SCHURECHT SPARK PLUG INSULATORS CONTAINING zno 4 Sheets-Sheet 2 Filed April 25, l952 I INVENTOR Harry G. c/vurecbf BY 100 F ATTORNEY Aug. 27, 1957 H. G. SCHURECHT 2,804,392

SPARK PLUG INSULATORS CONTAINING Z710 Y Filed April 25, 1952 4 Sheets-Sheet 3 vunmwxmw INVENTOR Harry G.-.Sc/1urechf BY a a 0M ATTORNEY g- 1957 H. G. SCHURECHT 2,804,392

SPARK PLUG INSULATORS CONTAINING Z110 Filed April 25, 1952 4 he -sheet 4 INVEN TOR Harry G. Jc/vureafif ATTO R N EYS This invention relates to electrical insulators which contain zinc oxide, and which-are suitable for spark plugs and for similar uses.

Zinc oxide has heretofore been suggested as a 'flux for use with high alumina spark plug insulator bodies,=as an alternative to a-lkaline earth compoundsfrequently used. Relatively satisfactory high alumina insulators can be produced using'zinc oxide in; the; proportions-in which fluxes are ordinarily employed. When 'the'propo'rtion of zinc oxide is increased above that usually 'employedas a flux, however, the'hotdielectric propertiesof the resulting insulators are i so, poor as "to, be unsatisfactory for :any

spark plug use. For example, an insulatormade from zinc oxide and alumina, in the proportions of about 25 nrol percent and about 75 mol percent, respectively, has an electrical'resis'tance of substantially'less than l megohm at 1350 F., measured as described in Example 1 hereof, and it is generally accepted that spark plug insulators for high compression engines "must-have a minimum resistance ofat least 1 megohm at 1350" F. to besati'sfactor-y. 1ncreasing the proportion of zinc oxide above 25. percent further decreases the electrical resistance of insulators containing it.

Thepresent invention is'b'ased upon the discovery that electrical insulators "meeting the exacting requirements for -u'se as spark plug insulatorsinhigh compression engines burninggleaded fuel can be produced from alumina-and zinc oxide when the 'latterispresent in higher proportions than heretofore employed, and that such sparkplug-insulators can also be produced from blends in certain proportions of zinc oxide with alumina, beryllia, magnesia, oxides of cerium, tin, zirconium, titanium, calcium; strontium, barium, and boron.

In the drawings,

Fig. 1 is a triaxial diagram showing the proportionsin mol percentages in which alumina, beryllia,and' ZnO can be used 'toproduce electrical insulators 'of'the invention;

Fig. 2 is a triaxial diagram showing the proportions in mol, percentages in which magnesia, -beryllia,and!ZnO can be used to produce electrical ins'ulatorsof the-invention; I

Fig. 3 is a triaxial diagram showing the proportions in United States Patent ice 2 mol percentages in which alumina, magnesia andZnO can be used to produce electrical insulators of the invention;

Fig. "4 is a regular tetrahedron showing the proportions inmol percentages in which alumina, beryllia,, magnesia, andZnO can'be-combined to produce electrical insulators of the invention;

Fig. 5 is another view of the tetrahedron shown in Fig; 4;

'Fig. 6' is a combined view of Figs. 1, 2, and 3, (in a reduced scale, illustrating the wa these three 'fi'gure's are combined to produce Figs. 4 and 5;

'Fig. 7 is a reproduction of Fig. 4 with lines added thereto to represent planes which identify-preferred com- 15' positions; and I Fig8 is a reproduction'ofFig. 4 withot'h'er line s added thereto to represent different planes which represent other preferred compositions.

According to the invention, asintered ceramic electrical insulator suitable for spark plug and similar-uses is provided. The electrical insulator shows, by chemical analysis, at least percent by weight of a major component having-a composition represented by the portion of Figs.,4 and 5 within the shaded planes,':a'nd from a trace to.40 percent by weight of a minor component. The minor component consists essentially. of atleast onemodifying ingredient that is an oxide of one of the following metals; calcium, strontium, barium, boron, titanium, z'ir- "conium, cerium and tin.

T n ul r q fi a na'ff b the minor component, not over 20 percent by weight-of oxides ofcalcium, strontium, and bariurn,not over s percent by weight of an oxide of boron, and not over 20 percent by Weight of oxides of titanium, zirconium, cerium and 'tin. The sum of the mols of oxides of titanium, zirconium, cerium, and tin is not more than half the sum of the 'mols'of'alu'rnina and magnesia plus one-twentieth the trials of *beryllia.

Referring "now more particularly 'to the drawings, the

shaded portion of Fig. 1, which represents compositions in mol percentages, shows the proportions in which alu- -mina, beryllia, and zinc oxide can be combined prior to firing to produce electrical insulators having sufliciently high resistance at elevated temperatures, and suiiiciently h'i'g'h'th'ermal conductivity, for use as spark plug insulators. it will be observed that this shaded area may be designated firing bodies of compositions represented by the upper portion of this shaded area, 14-1920 14, have exnamely high heat conductivities, and are, for this reason, preferred spark plug insulators. Electrical insulators produced by firing compositions represented bythe area and MgO, BeO, and ZnO (Fig. 2) are visible.

.3 The compositions represented by the several points of Fig. 1 are shown in Table A, below:

A and lie within the area 11--13-27-24--17-11. This area is not shaded in Figs. 4 and 5 because shade lines would unnecessarily complicate the figures, and would make comprehension diflicult. From the angle at which the tetrahedron of Fig. 5 is viewed the remaining surfaces which bound the operable area can be seen readily. These surfaces are as follows: 11161711; 2417- 1624; 24162024; and 2420-1924. All of Referring now to Fig. 2, electrical insulators produced I these identified areas are invisible, and are shaded with dotted lines, because they lie behind the faces of the tetrahedron. The surface representing ternary mixtures of BeO, A1203, and ZnO (Fig. 1) is visible in Fig. 5. The other two surfaces bounding the operable area (24-27-- 14-1924, Fig. 2, and 11-13272417-11, Fig. 3) can also be identified in Fig. 5.

Compositions represented by the portion of Fig. 4 inclosed by a plane through the points 14, 20, and 28, a plane through 14, 20, and 19, a plane through 14, 19, and 28, and a fourth plane through 19, 20, and 28 are preferred because electrical insulators fired therefrom have especially high thermal conductivities. Compositions represented by the portion of Fig. 4 between a plane through the points 40, 41, and 42 and a second plane through the points 44, 45, and 46 are also preferred because insulators therefrom have especially high electrical resistance at elevated temperatures.

represented by the area 14--192814 are preferred because they have especially high thermal conductivities, and insulators produced by firing compositions represented by the area between the lines 4041 and 44-45 are preferred because they have especially high electrical resistance at elevated temperatures Maximum thermal conductivities are obtained from compositions represented along the line 15-26. j

The compositions represented by the several points of Fig. 2 which are not given in Table A are shown in Table Referring now toFig. 3, the shaded area thereof, designated 1113-27-2417--11, represents compositions of alumina, magnesia, and zinc oxide which can be fired to produce electrical insulators having properties that make them suitable for spark plug and similar uses. The area between the lines 40-.42 and 4446 represents compositions which, when fired, have especially high electrical resistance at elevated temperatures. Point 17 represents a composition containing 60 mol percent of A1203, 20 mol percent of MgO, and 20 mol percent of ZnO.

Figs. 4 and 5 are two views of a tetrahedron representing the proportions of magnesia, beryllia. alumina, and zinc oxide operable for the production of electrical insulators of the invention. Fig. 5 shows the tetrahedron rotated counter clockwise 120 above a vertical axis V through the upper or BeO vertex from the position shown in Fig. 4. In Fig. 4, the faces of the tetrahedron representing ternary mixtures of A1203, BeO, and ZnO (Fig. 1), A third boundary of the operable proportions faces the observer, but is hidden by the two faces of the tetrahedron; this surface is shaded with dotted lines, and is designated 13-1427-13. Operable compositions containing alumina, magnesia, and ZnO are also represented in Fig. 4

Still another group of preferred compositions represented on Fig. 7 lies between a plane through the points 25, 19, 11 and a second plane through the points 25, 14 and 13.

Fig. 6 shows the tetrahedron of Figs. 4 and 5 with its three faces which meet at the BeO vertex rotated about their respective base lines opposite the BeO vertex into the plane of the base of the tetrahedron. It will be apparent from observation of Fig. 6 that Figs. 1, 2, and 3 are represented therein; from this it is apparent that the tetrahedron of Figs. 4 and 5 is derived from Figs. 1, 2, and 3. It is known that the compositions which result from mixing, in all proportions, two mixtures represented by two points ona triaxial diagram are represented by a straight line joining those two points. Similarly, the compositions which result from mixing, in all proportions, two binary,

ternary or quaternary mixtures represented on a regular tetrahedron, are represented by a straight line joining those two points. It follows, therefore, that the plane in Fig. 4 through the points 13, 14, and 27, for example,

represents the compositions .of mixtures, in all proportions, of a binary blend of alumina and zinc oxide reprer sented by the point 13, a binary mixtures of beryllia and zinc oxide represented by the point 14, and a binary mixture of magnesia and zinc oxide represented by the point 27. 'From the foregoing it follows, also, that the portions of Figs. 4 and 5 bounded by the shaded planes represent mixtures in all proportions of compositions represented blends of the two compositions will also produce insulators satisfactory for spark plug uses.

Bodies 31, 32, and 36 from Table II, below, demonstrate this principle, as

do bodies 1, 4, 5, 36, 38, 40, 41, 43, 44, and 45, from Tables I and II, below.

The suitability :for use in the manufacture of electrical insulators for spark plug purposes of various compositions within the portion of Figs. 4 and 5 bounded by the shaded 'planes, and containing additives or modifying oxides within the proportions stated above, was demonstrated by preparing several insulators, and testing the properties of each. Compositions and properties for various insulators within the scope of the claims are given in the following examples, which are to be construed as illustrative only, and not as limiting the invention.

Example 1 Sintered ceram'irelectrical insulator-swere prepared mar y lil and zinc oxide, plus minor'amounts of airefide of carfrom various compositions including a cium, strontium,-or-barium introduced -incidenta1ly in -the course of processing. In -a1lcases, ablend'-of- -at least two of the three -named ingredients -was- -wet milled to substantial uniformity (usually: for 18 hours' -=wasathen dried and mixed with 4--percent-bf 'parafiin' -wax, based upon the weight of dry"ingredieiitsjdissolved in carbon tetrachloride. The--waX-was-thoroughly mixed with-the dry ingredients, and'the carbon'ttrachloride ,volatilizd, leaving the wax uniformly dispersed throughout the comnh-nes porosity, strength and other properties. This was .-..measured .by. a standard dye .test. Inthe tablesherein,

10 ture.

Typical test results for bodies produced from-two br more of the three named ingredients are presented in i Table 'I,-blow':

TABLE I H 'ElectricalRe- M01 Percent Dye Test sistance. Thermal Dtflu- Body, (Megohms) I sivity, Seconds N0. at 1,350" F.

BeO A120; ZnO Gone 16 0011631 Gone 16 Gone 31 Gone 16 cone-s1 .,6.9 8.7 100+ 9.20 23.3 29.2 100+ I 17.40 1 17.5 11.0 12 100+ 18.5 11.8 3.6 21.5 I I 8.5 11.1 86:0 15.1 .F 6 "100+ 26.9 17.0 4.4.4 55.6 .1 100+ 100+ 24.0 39.5 60.5 24.8 24.9 4351.6 65.4 100+ .L 20. 9 23. 5 34.9 64.1 100+ 31.4 l

position. Test cyliride'rs; about V2 inch in diameter arid If, for purposes of comparison, but not in'"acc0rdaii'ce approximately /1 inch inlength;- were-then-pressed from "with the invention, insulators are producedas described the mixed composition usingfa total pressure 6f .ten thousand pounds. 'These cylinders -were-then fired to Cone 16 or to Cone 31.- '-Thebodies soprepared were tested to determine their suitability for use as spark plug to acer'tain 'extentupon the'desig'n of'th plug; 'thejminirnum acceptable-value should'be at least 1' 'meg'iohr'rr fat 1350 F. for such cylinders. Another standardtest was 45 conducted to compare the thermal diffusivities of insu lators produced from the difierent compositiohsz thetest above from" compositions containing "83.4 mol percent ofiZriO; 45.5 mol per cent of Zn'O, and 23.8 mol percent 'of -ZnO,'ba'lance alumina,- in each instance the-electrical resistance at 1350 F. is found to be less than 1 megohm. Such insulators, accordingly, are not suited for spark plug uses. Similarly, insulators containingmore than 16 /3 molpercen't, and up to 72.7 mol percent,"'o'f beryllia, same-"alumina,- arerelatively unsatisfactory for/spark ,plng pu'rr'aoses. p

For purpos'es of comparison, the characteristics "of substantially pure zinc oxide insulators, prepared as described above, are also presented in Table C, below:

involved placing a crystal of citric acicl'onon'e and ef'flre' sintered /z in'ch cylinder, and immersing the'otherend inch. QThe nu'm'ber of 7 seconds required for heat conducted through the insulator to melt the citric acid cfry'stal, which--melts-at-307.4 R, is reportedin-tlie tables:-

hereinas fthermal difiusivity, andis an inverse function of thermal-condu'ctivity. Tobe satisfactory for spark plug use an insulator sliduldhave amermsi diffusivity, .so measured, notv greaterthan ill-seconds, and preferably tn'ot greater than-40 seconds. The adequacy of the firing under a" senor standard eonditiohs is also an 'iiirr'porta'nt characteristic of a ceramic composition since it deter- 65 "ITable'II; below,:presents typical test results obtained with'b'odies containing varying proportions of A1203,

' "BO,-Zn O, and various additives, and demonstrates, in

conjunction with Table I, the general proposition that where a'body has been produced containing two or more -ofthe'principal ingredients, A1203, 'B'eO, ZnO, and MgO,

a satisfactory body can be produced from these ingredients in the same proportions, but containing small amounts of the additives or modifying ingredients claimedherein. In all insta'nces,the' bodies reported in a Table :IIwere'produced inthe' same way as the bodies reported in Table I.

i i 7 TABLE 11 I Electrical Resist- Thermal Diflu- Mol Percent Additives, Grams per ance ego sivity, Seconds Dye Test y 1,000 grams BeO, at 1,350" F. V

N o. A110; and ZnO BeO A120: ZnO Gone 16 Gone 31 Gone 16 (June 31 Gone 16 Gone 31 L 7. 5 Whiting 15.5 grams 100+ 100+ 5. 8 Mat. 7. 5 15.5 grams each of Whlt- 100+ 95 5. 6 Mat.

ing and Bentonite. 7. 5 90 100+ 5. 9 Mat. 14. r 0 9 0. 7 Mat. 17.0 Y i 8 7.0 Mat 15.5 grams Bentonite 17 92. 7. 5 25.9 grams ZrO: 1. 5 11 5.7 Mat.

81.0 grams Whiting 98.7 z 1.3 .0 A* 100+ 100+ 8.0 Mat. 97.0 3.0 136.8 A. 55 58 6. 4 S. U. F. 95.0 5.0 55 55 11.7 S. F. 98. 8 1.2 100+ 100+ 6. 7 Mat. 97. 4 2. 6 100+ 100+ 6. 5 Mat 95. 6 4. 4 32 33 6. 6 Mat 98.9 1.1 100+ 6.0 97. 6 2. 4 72 6. 5 96.0 4.0 6. 7 98.4 1.6 90 6.9 96.3 3. 7' 28 6. 9 93.8 6. 2 .3. 7. 2 98.0 2.0 38 6.3 22. 6 54. 8 22. 5 100+ 29. 7 28.6 43.5 27.7 100+ 24.1 28.8 35.6 35.6. 100+ 100+ 38.2 34.6 32.1 23.8 37.1 25.8 27.0 100+ 17.7 41. 0 18. 2 40. 7 90 16. 8 47. 7 26. l 26. 1 v 92. 5 100+ 19. 2 13. 8 Mat. 53.9 20.0 26.0 (*3 100+ 100+ 15.9 Mat. 61.0 19. 4 19. 4 72.3 100+ 16. 7 9.4 Mat. 72. 3 9. 9 16. 9 C) 100+ 9. 0 8. 5 Mat. 76. 7 15. 3 8. 1 95 85 10. 5 Mat. 84. 5 7. 7 7. 7 92. 5 100+ 10. 4 5. 8 Mat. 89. 5 5. 3 5. 3 66. 0 100+ 9. 4 5. 8 Mat 93. 6 3. 2 3. 2 92. 5 100+ 8.33 6.0 Mat 96. 9 l. 5 1. 5 70.0 100+ 5. 3 Mat.

Indicates that additives consisting or 15.5 grams whiting, 20.7 grams of talc, and 15.5 grams of bentonite were mixed with 1,000 grams of the indicated composition. When a number is followed by a letter and an asterisk, the number indicates the number 01 grams of a modifying ingredient referred to by the letter mixed with 1,000 grams of the composition, and the asterisk indicates whiting, talc, and bentonitc in the quantities stated above. A refers to ZIOz; B to SnOz; O to CeOz "Body 30 contained 104 grams of whiting and 21.6 grams of talc per 1,000 grams of BeO and Zn Example 3 In addition to the representative bodies in Tables I and II wherein alumina was employed, other bodies containing at least two of the ingredients ZnO, BeO, and MgO and D to T102.

i presented in Table III, below.

In all instances, the insulators were prepared in the manner described in Exhave been produced to demonstrate the operability of ample 1.

TABLE III Electrical Resist- Ihermal Difiu- M01 Percent Additives, Grams per anee (Megohms) sivity, Seconds Dye Test Body No. 1,000 grams BeO, at 1,350 F.

MgO, and ZnO BeO MgO ZnO Gone 16 Gone 16 Gone 31 Gone 16 Gone 31 40 05. 5 2.2 2.2 0.4 Mat. 47..-. 00. 5 4. 7 4. 7 6. 8 Mat. 48 21. 8. 47.3 21.0 30.9 49 18. 3 56. 5 24. 2 22. 9 Milt. 50 17. 2 66. 2 16. 6 29. 8 51 12.3 75.4 12.2 29.2 52 8.0 83.9 7.9 (g 23.7 53 3.9 92.0 3.9 22.6 54 97.9 2.1 24.4 55.. 95. 3 4. 7 30. 8 56 92.2 7.8 33.3

34.6 24.9 100+ at 1,100 F..

Indicates that additives consisting of 15.5 grams whitin grams of the indicated composition. When a number is fol g, 20.7 grams of talc, and 15.5 grams 0! bentonite were mixed with 1,000 lowed by a letter and an asterisk the number indicates the number of grams of a modifying ingredient referred to by the letter mixed with 1,000 grams of the composition, and the asterisk indicates whiting, talc, and bentonite in "Body 66 was not tested above 1,100 F.

the quantities stated above. A refers to ZrOs; B to SnOr; and O to GeOa.

ssence:

. 6 Example 4 'nxam ies bf-bodies containing A12o ,.M o. and ZnO are presented in Table IV, below. In eachinstancethe .bodies wereprepared bya procedure identical that described in Example 1.

cent by -weight-iofi a major com onent having a composi- "tion represented 'by" the'portion of Fi'gs94 and S of "the attached drawings within the shaded planes, and. from a trace .to 40 percent by weight-of a: minor component-consisting essentially of at least one-metaloxide "modifying TABLE -IV Additives, .nnmmrmsut- 'TherrnalDifiu .Mol-Percent Grams per ance-(Megohms) --sivity, Seconds Y "Body'No. 1,000 grams 5 Dye Test,

. A 1z0a,Mg0 Gone 16 and- ZnO v A I A110; *MgO ZnO Oone'IG Gone 31 Gone 16 Gone 31 2.3 95.1 2.3 g) 100+ 23.7 14.8 Mat. .49 1190.0 4.9 100+ 98 27.3 17.0 Mat. 7.9 84.1 7.9 v 100+ 100+ 31.3 202 Matt. 11.4 77.4 11.3 ('g 100+ 98 j33;4 22.3 Mat.

114.3 .70.3 :15.4 100+ 36.6 530.5 8. F. 19.9 -6032 19.9 -92 100+ ..40.8 -.28.1 -S.;U. F. "27.9 "47.6 24.4 ""38 100+ "28.1 17.3 S.U.F. 34.5 34.8 30.7 50 85 "2928 25.8 SJU; F. 42.5 19.3 38.2 100+ 29.4 -21.7 Mat. .58. 1 20.9 20.9 f) 19 100+ '47.8 U'.F. 47.2 "26.4 26.4 g 95 100+ 1543.9 1 U. F. 37.2 31.3 31.3 100+ 30.7 124.5 .Mat.

Indicates that the additives eonsisted of-15.5 grams ofwhiting; 20.7 grams ottaic, and 15.5 grams of bentonite per 1,000 grams of A1103, MgO and ZnO.

Example Insulators were'gprepared' containing various proportions of BeO, A1 0 MgO and ZnO. the insulators were prepared according to the: procedure described inExample 1. Compositions and test results are presented in Table V, below.

In each instance.

l by weight of an oxide ofboron, not more than percent by weight of a refractory oxide selected from the group TABLE V Additives, Electrical Resist- Thermal Difiu- Mol Percent Grams per ance (Megohms) sivity, Seconds Dye Test Body No. 1,000 grams BeO, A1105, MgO and BeO A1103 MgO ZnO ZnO Gone 16 Gone 31 Gone 16 Gone 31 Gone 16 Gone 31 47. 3 16. 1 16. 1 20. 4 l4. 9 14. 40 Mat--. Mat 39. 6 5. 6 35. 8 l9. 0 1 16. 2 l6. 4 Mat... Mat; 22. 9 5. 8 55. 5 15. 8 82 23. 3 22. 2 Mat-.... Mat. 58. 9 10. 6 17. 1 13. 3 0) 100+ 12. 5 l2. 5 Mat. Mat. 43. 6 11.0 35. 1 10.2 100+ 15. 6 15. 4 Mat Mat. 62. 4 15. 8 16. 7 5. 0 100+ 100+ 13. 0 U. F-- Mat Indicates that the additives consisted of 15.5 grams of whiting, 20.7 grams of talc, and 15.5 grams of bentonite per 1,000 grams oi BeO, A1201, MgO and ZnO.

It will be noted by reference to Tables I and H, above, consisting of titanium, zirconium, cerium and tin, and

that bodies fired from binary mixtures of BeO and ZnO within the limits claimed herein are particularly advantageous, because they have wide firing ranges, many such bodies being matured when fired either to cone 16 or to cone 31. Specifically, insulators composed predominately of ZnO and BeO in ratios of 1 mol of ZnO to from 4 to 300 mols of BeO, are preferred; most desirably, the ratio is 1 mol of ZnO to from 4 to 13 mols of BeO. Another group of preferred insulators within this group has a composition of at least 80 mol percent of BeO and at least l a mol percent of ZnO.

It is to be understood that the invention is not limited to the use of pure oxides, as carbonates, hydroxides, and other compounds which yield the oxides upon firing are equally operable. For example, Mg(OH) Al(OH) MgCOg, ZnCO and the like, can be used instead of A1 0 ZnO, and MgO. When such compounds are used instead of the oxides, they should be used in proportions such that the fired insulator contains the oxide in the proportions set forth herein.

This application is a continuation in part of application Serial No. 766,648 filed August 6, 1947, now abandoned.

Having described the invention, I claim:

1. A zinc oxide containing sintered ceramic electrical insulator showing by chemical analysis at least 60 perwherein the sum of the mols of oxides of titanium, zirconium, cerium and tin is not more than half the sum of the mols of alumina and magnesia plus one-twentieth the mols of beryllia.

2. A sintered ceramic electrical insulator as claimed in claim 1 in which the composition of the major component is represented by the shaded area of Fig. 1 of the attached drawings.

3. A sintered ceramic insulator as claimed in claim 1 in which the composition of the major component is represented by the shaded area of Fig. 2 of the attached drawings.

4. A sintered ceramic electrical insulator as claimed in claim 1 in which the composition of the major component is represented by the shaded portion of Fig. 3 of the attached drawings.

5. A sintered ceramic electrical insulator having a high hot dielectric value and high heat conductivity which is composed as shown by chemical analysis, of at least 60 percent by weight of ZnO and BeO in ratios of 1 mol of ZnO to from 4 to 300 mols of BeO.

6. A sintered ceramic electrical insulator having exceptionally long firing range which is composed, as shown by chemical analysis, of at least 60 percent by weight of ZnO and BeO in a ratio of 1 mol of ZnO to from 4 to 13 mols of BeO.

7. A sintered ceramic electrical insulator having a composition by chemical analysis of at least 80 mol percent BeO and at leastl/s mol percentof ZnO;

8. 'A sintered ceramic electrical insulator having a composition by chemical analysis of at least 20 mol per- .cent of A1203 and at least 50-mol percent of ZnO. ,v

composition by chemical analysis of at least 60 molflper-t cent of MgO and at least /3 mol percent of ZnO.

11. A sintered ceramic electrical insulator having a mol percent,

wherein the sum of the mols of oxides of titanium, zirconium, cerium and tin is not more than half the sum of the mols alumina and magnesia plus one-twentieth the mols of beryllia. 7

13. A sintered ceramic electrical insulator which consists essentially of at least 60 percent by weight of a major component having a composition represented by the portion of Fig. 8 of the attached drawings lying between a plane through the points 40, 41, 42 and a second plane through the points 44, 45 and 46, and from a trace to 40 percent by weight of a minor component consisting essentially of at least one metal oxide modifying ingredient selected from the group consisting of oxides of calcium,

titanium, zirconium, cerium and tin, but not over 20 percent by weight of calcium oxide, and not over 20 percent by weight of the four last-named oxides, and wherein high hot dielectric value which is composed predomi- 12. A sintered ceramic electrical insulator which consists essentially of at least 60 percent by weight of a major component having a composition represented by theportion of Fig. 7 of the attached drawings lying between a plane through the points 25, 19, 11, and a second plane through the points 25, 14, and 13, and from a trace to 40 percent by weight of a minor component consisting essentially of at least one metal oxide modifying ingredient selected from the group consisting of oxides of calcium, titanium, Zirconium, cerium and tin, but not over 20 percent by weight of calcium oxide, and not over 20 percent by weight of the four last-named oxides, and

the sum of the mols of oxides of titanium, zirconium, cerium and tin is not more than half the sum'of the mols alumina and magnesia plus one-twentieth the mols of beryllia.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A ZINC OXIDE CONTAINING SINTERED CERAMIC ELECTRICALL INSULATOR SHOWING BY CHEMICAL ANALYSIS AT LEAST 60 PERCENT BY WEIGHT OF A MAJOR COMPONENT HAVING A COMPOSITION REPRESENTED BY THE PORTION OF FIGS. 4 AND 5 OF THE ATTACHED DRAWINGS WITHIN THE SHADED PLANES, AND FROM A TRACE TO 40 PERCENT BY WEIGHT OF A MINOR COMPONENT CONSISTING ESSENTIALLY OF AT LEAST ONE METAL OXIDE MODIFYING INGREDIENT, WHEREIN THE MINOR COMPONENT IS COMPOSED OF NOT MORE THAN 20 PERCENT BY WEIGHT OF A FLUX SELECTED FROM THE GROUP CONSISTING OF AT LEAST ONE OXIDE OF CALCIUM, STRONTIUM AND BARIUM, NOT MORE THAN 5 PERCENT BY WEIGHT OF AN OXIDE OF BORON, NOT MORE THAN 20 PERCENTT BY WEIGHT OF A REFRACTORY OXIDE SELECTED FROM THE GROUP CONSISTING OF TITANIUM, ZIRCONIUM, CERIUM AND TIN, AND WHEREIN THE SUM OF THE MOLS OF OXIDES OF TITANIUM, ZIRCONIUM, CERIUM AND TIN IS NOT MORE THAN HALF THE SUM OF THE MOLS OF ALUMINA AND MAGNESIA PLUS ONE-TWENTIETH THE MOLS OF BERYLLIA. 